The purpose of this research is to determine if there is a lawful emergence of certain cognitive and affective phenomena during the period 6 through 21 months of age in the human infant. The basic hypothesis the research seeks to affirm or refute is that there is a major change in cognitive functioning during the last third of the first year and that the cognitive processes that emerge during this time are responsible for stranger and separation fear, object permanence, and changes in patterns of attentiveness and reaction to discrepant events.